django 查询集 select_related 。 values() 重命名键

Posted 2023-02-23

【中文标题】django 查询集 select_related 。 values() 重命名键

【英文标题】：django queryset select_related . values() rename key

【发布时间】：2018-10-23 18:02:57

【问题描述】：

使用python3.4 django 2.0.2

models.py

class Userinfo(models.Model):

    useruid = models.BigAutoField(db_column='UserUID', primary_key=True)

    useremail = models.CharField(
            db_column='UserEmail', unique=True, max_length=100)
    userpassword = models.CharField(db_column='UserPassword', max_length=128)

    passwordsalt = models.CharField(db_column='PasswordSalt', max_length=128)
    userstatus = models.IntegerField(db_column='UserStatus', default=0)
    username = models.CharField(
        db_column='UserName', max_length=100, default=0)
    class Meta:
        managed = False
        db_table = 'userinfo'

class Postinfo(models.model):
    postuid = models.BigAutoField(db_column='PostUID', primary_key=True)
    content = content = models.TextField(db_column='Content')
    useruid = models.ForeignKey(
    Userinfo, db_column='UserUID', on_delete=models.CASCADE)

    class Meta:
         managed = False
         db_table = 'postinfo'

查询集

postquery = models.Postinfo.objects.all().select_related("useruid").order_by(
                '-postuid')

后查询是

<QuerySet ['content': 'test','postuid': 1, 'useruid_id': 1,OtherPosts...>

和

userinfoquery = postquery.values("useruid_id__username","useruid_id__userstatus","useruid_id")

用户信息查询是

 <QuerySet ['useruid_id__username': 'firstuser','useruid_id__userstatus': 0, 'useruid_id': 1,OtherUsers...>

我想要 useruid_id__username -> 用户名

useruid_id__userstatus -> 用户状态

useruid_id -> useruid

我试过了

userinfoquery = postquery.values(
                useruid="useruid_id", username="useruid_id__username", userstatus="useruid_id__userstatus")

此代码引发异常

QuerySet.annotate() received non-expression(s): useruid_id, useruid_id__uesrname, useruid_id__userstatus.

如何删除 useruid_id__

【参考方案1】：

从 Django 1.11 开始，您可以将表达式与 values() 一起使用，请检查 release notes。因此，您需要在查询中添加F 表达式：

from django.db.models import F
userinfoquery = postquery.values(
                useruid=F("useruid_id"), username=F("useruid_id__username"), userstatus=F("useruid_id__userstatus"))

【讨论】：

引发此异常The annotation 'useruid' conflicts with a field on the model. useruid 不在 postquery.values() 中

【参考方案2】：

你可以使用注释功能

from django.db.models import F

Postinfo.objects.annotate(renamed_value=F('useruid_id__username')).values('renamed_value')